Some measurement systems, such as a chromatograph system or a spectroscopic analyzer, produce measurement data in the form of waves with one or more peaks. In those systems, the result of a measurement is analyzed by determining the width, intensity, area and other values of a peak waveform of the measurement data by waveform processing including the steps of determining the rising and falling points of the peak, setting the baseline, and calculating a fitting curve using a Lorenz distribution function or Gaussian distribution function (see Patent Literature 1).
Correct determination of the rising and falling points of a peak is important since these points affect the value of the peak area. In a preparative chromatography, in which a specific target component in a sample being analyzed is preparative-separated based on the result of a chromatographic measurement, it is necessary to correctly determine the rising and falling points of the peak by waveform processing so as to minimize the amount of unwanted components to be mixed with the target component.
In a chromatograph system, two parameters called “Width” and “Slope” are used in the determination of the rising and falling points of a peak.
The parameter “Width” is the smallest value of the full width at half maximum (FWHM) by which a peak is identified in the waveform processing; a waveform whose FWHM is smaller than this value is identified as noise. The parameter “Width” is expressed in the same unit as the horizontal axis of the measurement data, e.g. in minutes as in the case of a chromatograph system or in 1/cm (or nm) as in the case of a spectroscopic analyzer. Therefore, users can intuitively determine whether or not the “Width” value is appropriate.
The parameter “Slope” is the critical value of the slope of a peak for locating the rising or falling point of the peak; the point at which the slope of the peak is equal to the critical value and around which the slope of the peak shows a predetermined increasing or decreasing tendency is identified as the rising or falling point of the peak. The parameter “Slope” is expressed in a complex unit in which the units of the horizontal and vertical axes are composed. Therefore, it is difficult for users to intuitively determine whether or not the “Slope” value is appropriate.
With such a technical background, efforts have been made to automatize the determination of the values of the two parameters (in particular, the determination of the “Slope” value) using a computer. In one method for determining an appropriate value of the “Slope”, a recommended value of the “Slope” for a peak waveform of measurement data is automatically calculated by determining the baseline of the waveform with a predetermined criteria. In another method, the rising and falling points of an actual peak is calculated by an analysis using predetermined values of the parameters “Width” and “Slope.”
The automatic determination of the values of the parameters “Width” and “Slope” using a computer is a standardized process and does not allow the rising or falling point of the peak to be arbitrarily selected as needed by users. For example, in a preparative chromatography, when a component other than a specific component has been found to be mixed in a preparative-separated sample, the user may desire to set the rising point of a peak at a later point in time and/or the falling point at an earlier point in time. However, the automatized process using a computer cannot flexibly deal with such situations. In such cases, the user needs to directly specify the values of the parameters “Width” and “Slope.”
However, specifying the value of the parameter “Slope” is difficult for those who are not accustomed to an analysis for the waveform processing. This is because, as explained earlier, it is difficult for users to intuitively determine whether or not the “Slope” value is appropriate.
In a component analysis using spectra, there is the case where a plurality of spectra which only differ from each other in peak intensity need to be superposed on each other for comparison. In this case, a spectrum whose peak intensity is lower than those of the other spectra may be obscured in the vicinity of the baseline. When the user directly specifies the values of the parameters “Width” and “Slope” and determines the rising and falling points of a peak in such a low-intensity spectrum, it is difficult to determine, from the screen display, whether or not the rising and falling points of the peak are appropriate. Therefore, the user needs to perform the cumbersome task of expanding the vertical axis of the spectrum whose peak intensity is low and then determining the rising and falling points of the peak by directly specifying the values of the parameters “Width” and “Slope.”